The scientific core is responsible for all of the particles that will be studied in the center. These responsibilities include thorough chemical and physical characterization of all particles, synthesizing new particles for the purposes of completing libraries and for introducing new functionality such as fluorescence, and designing and synthesizing highly specialized particles that will be used to test hypotheses arising from the in vitro and in vivo biological studies about injurious effects at the nano-bio interface. Accurate, thorough and interpretable characterization of Engineered Nanomaterial (ENM) libraries (Table 1) is an absolute necessity for studies of pulmonary toxicity. The physical and chemical properties must be delineated in order to provide a basis for interpreting molecular and cellular injury mechanisms. Manufacturers' statements about the properties of the materials that they ship provide varying degrees of completeness and accuracy. The Scientific Core will carry out all of its own measurements (see section IB) and provide reliable data in a uniform arid interpretable fonnat to the project leaders.